Methods to utilize ultrasonic energy to reduce the initial contact forces in known-good-die or permanent contact systems

ABSTRACT

A machine and method for bonding puncture-type conductive contact members of an interconnect to the bond pads of a bare semiconductor die includes the use of one or two ultrasonic vibrators mounted to vibrate one or both of the die and interconnect. A short axial linear burst of ultrasonic energy enables the contact members to pierce hard oxide layers on the surfaces of the bond pads at a much lower compressive force and rapidly achieve full penetration depth.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 09/921,621,filed Aug. 3, 2001, now U.S. Pat. No. 6,419,143, issued Jul. 16, 2002,which is a continuation of application Ser. No. 09/416,248, filed Oct.12, 1999, now U.S. Pat. No. 6,296,171 B1, issued Oct. 2, 2001, which isa continuation of application Ser. No. 09/027,690, filed Feb. 23, 1998,now U.S. Pat. No. 6,045,026, issued Apr. 4, 2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to electrical connections tosemiconductor devices. More particularly, the invention pertains tomethods and apparatus for making nonpermanent and permanentlow-resistance interconnections between a semiconductor device (die) anda substrate.

2. State of the Art

As the densities of input/output (I/O) wire bond pads increase onsemiconductor devices, testing of the devices becomes more difficult.The function of any interconnect system, whether a probe card, testsocket, or bum-in socket, is to provide a reliable interconnect betweenthe integrated circuit tester and the individual semiconductor device.The reliable bum-in and testing of bare dice is required to provideknown-good-die (KGD) for incorporation into multi-chip assemblies, forexample. The KGD testing of dice and wafers is dependent upon uniformlyachieving consistent electric connections between the test apparatus andthe semiconductor device substrate.

Prior art contact members for testing dice are generally of four forms.In one form, the contact members simply abut the bond pads or leads andthe two are pressed together to make the desired electrical contact.Examples of this type of interconnection are described in U.S. Pat. Nos.5,406,210 of Pedder, 5,572,140 of Lim et al., 5,469,072 of Williams etal. and 5,451,165 of Cearley-Cabbiness et al.

A problem with such connections is that bond pads are typically coveredwith a layer of metal oxides or silicon dioxide which insulates the padsand makes simple contact ineffective as a reliable electricalconnection. In some cases, differential thermal expansion of the contactmember may cause lateral movement which tears the bond pad.

In a second configuration, contact members may be formed to make a“wiping action” contact with the bond pads. Examples of such are varioussockets, pins, plugs, etc. Again, as is well known in the industry,pre-existent oxides and subsequently formed oxides on the metal surfacesresult in defective electrical contact.

In a third form of making temporary contact between a test device and adie, the contact members are nonpermanently bonded to the pads on thedice by a solder or other conductive bonding material. Illustrative ofthis configuration is the disclosure of U.S. Pat. No. 5,517,752 ofSakata et al. Removal of the solder (by remelting) is required todisconnect the contact members from the dice after testing is completed.

The use of solder reflow technology for temporary bonds has manydisadvantages including the following. First, surface preparation withhighly corrosive and environmentally hazardous fluxes is required.Second, solder bonds are occasionally defective, requiring testing ofeach bond and reworking if necessary. Third, solder reflow requiresseveral additional processing steps and apparatus, adding to themanufacturing expense. Fourth, the temperatures required for reworkingas well as disconnect melting place additional stresses on the device.

A fourth form of contact member is configured to puncture a bond pad,passing through an oxide layer into the underlying metal forlow-resistance electrical contact. An example of this configuration isshown in U.S. Pat. No. 5,506,514 of Difrancesco, incorporated byreference herein.

One preferred form of a puncturing contact member is described in U.S.Pat. Nos. 5,326,428 of Farnworth et al., 5,478,779 of Akram, and5,483,741 of Akram et al., all of which are incorporated by referenceherein. In this configuration, the interconnect has a non-conductive orsemiconductive substrate upon which raised contact members include sharpprojections for puncturing the metal oxide coating on the bond pads andretaining non-permanent, low-resistance electrical continuity with theunderlying metal. A compressive force is maintained during the time thedie or dice are undergoing testing. The sharp projections may be formedto limit the penetration distance.

Generally, the metal oxide layer overlying the metal is much harder thanthe metal. Thus, the force required to penetrate and pass through theoxide layer is considerably greater than the forces required topenetrate the metal.

The compressive force exerted on the interconnect and the semiconductordie may be controlled by (a) controlling the rate of movement towardeach other, or (b) controlling the compressive force itself, such aswith a spring or other such device. In either case, the initially highresistance requiring a high compressive force to penetrate the oxidelayer is suddenly released upon penetration. However, the compressiveforce may not be reduced to avoid “over-penetration” of the underlyingmetal. Furthermore, even small differences in the thickness of the oxidelayer will result in oxide penetration at different compression levels.The required compressive force to achieve oxide penetration of all bondpads will vary from die to die, further exacerbating the problem. Suchis particularly a problem where the die has a large number of bond padsthereon and the compressive force required to penetrate any oxidecoating on the bond pads is larger than that capable of beingtransmitted through the head of the transfer apparatus.

As is well known in the art, ultrasonic vibration has been used to joinbond pads and leads with thin wires. U.S. Pat. Nos. 5,494,207 and5,607,096 of Asanasavest and U.S. Pat. No. 4,475,681 of Ingle teachparticular ultrasonic wire bonding apparatus and methods. Ultrasonicvibration may be combined with heating as in the “thermosonic” wirebonding process. U.S. Pat. No. 3,697,873 of Mazur describes a method forultrasonically soldering contacts and indicates that “the ultrasonicwave energy acts to break up oxides on the surface of the semiconductorbody . . . .”

U.S. Pat. No. 3,938,722 of Kelly et al. discloses an apparatus usingultrasonic energy for forming bonds between beam leads and conductivesurfaces such as on a substrate.

SUMMARY OF THE INVENTION

The invention comprises an apparatus and method for reducing thecompressive force required to achieve the desired initial penetration ofa bond pad by a contact member, such as used in a die bum-in and testingcarrier. The high initial force required in the prior art to breakthrough the “crust” of hard oxide on the surface of the metal pad ismuch reduced. Penetration of the hard oxide layer ordinarily results ina sudden “rebound” of accelerated movement due to reduced resistance,and the contact member may overpenetrate the bond pad. However, withthis invention, the rebound is minimized, if not eliminated.

The maximum compressive force required to achieve the final desiredpenetration of the bond pad is also reduced, while ensuring that all ofthe bond pads on a bare die are fully penetrated to provide uniformlylow-resistivity interconnections.

In the invention, ultrasonic vibration is applied to either one die orboth of the bare dice and the corresponding interconnect contact member.The vibratory movement is generated in a direction generallyperpendicular to the die surface by a transducer including, e.g., apiezoelectric element. This direction of vibratory movement is knownherein as the “axial” direction.

The frequency and amplitude of the vibratory forces are controlled suchthat the interconnect contact member pierces the hard oxide layer on thebond pad very rapidly and at lower applied compression forces. Theultrasonic vibration also ensures that all bond pads are fullypenetrated to achieve low-resistivity interconnections.

The bonding system of the invention permits the use of low bondingcompressional forces together with generally unidirectional ultrasonicvibrational energy and a frequency-modulated, controlled resonance toproduce uniformly reliable simultaneous connection of all bonds on a diewithout heat or with minimal heating.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The invention is illustrated in the following figures, wherein theelements are not shown to scale.

FIG. 1 is a cross-sectional end view of a bonding apparatus of theinvention in an assembler machine;

FIG. 2 is an enlarged cross-sectional view of contact members of asemiconductor device and an interconnect test apparatus prior to bondingof the contact members with the method and apparatus of the invention,as found within area 2 of FIG. 1;

FIG. 3 is an enlarged cross-sectional view of contact members of asemiconductor device and an interconnect test apparatus followingbonding of the contact members with the method and apparatus of theinvention; and

FIG. 4 is a generalized graphical depiction of the bond pad penetrationas a function of applied force with and without the ultrasonic vibrationof the invention.

DETAILED DESCRIPTION OF THE INVENTION

An improvement in forming a non-permanent or permanent low-resistivityelectrical connection between a penetration-type raised contact memberand a conductive bond pad of a bare die is described herein. Theinvention is particularly applicable to systems for testing bare dice tobe referred to as known-good-dies (KGD), where the testing interconnectis re-used many times.

The invention is described herein in relation to a testing apparatus orassembler whereby one or more bare dice (singulated or in a wafer form)are non-permanently interconnected with a test device, but the inventionmay be used for making other temporary or permanent electricalconnections between a bare die and a substrate with any desired typecontact member or a puncture-type contact member.

As depicted in FIG. 1, an assembler machine 10 is shown in part andincludes a die mount or quill 12 to which a bare die 14 is secured onits back side 16 by a vacuum formed through apertures 18 of the quill12. The vacuum may be applied either through one aperture 18, aplurality of apertures 18, a quill 12 having a metallic tip, a quill 12having a resilient tip, or variations thereof. The active surface 20 ofthe die 14 is shown with a plurality of bond pads 22 for connection touseful electronic circuits, as known in the art. Facing the activesurface 20 of the die 14 is an exemplary interconnect 24 including asubstrate 26 having a connection surface 28 with a plurality of raisedcontact members 30. The contact members 30 are located on the connectionsurface 28 for accurate contact with corresponding bond pads 22 on theactive surface 20.

The interconnect 24 is here exemplified as a die tester, i.e., a diecarrier used for burn-in and testing of dice for KGD purposes or a“probe card” used for testing purposes, having its rear side 38 mountedon a support member 32 by any suitable means 34 extending between theinterconnect 24 and the support member 32. Alternative methods ofmounting the interconnect 24 and/or die 14 include mechanical retainingmembers and the like as known in the art.

The quill 12 supports the die 14 and may be lowered in axial direction40, i.e., parallel to centerline 42, whereby the die 14 and interconnect24 meet and are electrically joined by a controlled compressive force indirection 40. The term “interconnect 24” is used herein as being ageneric term for any device having contact members 30 which aresimultaneously connected to the bond pads 22 of a die 14. The machine 10may include means for controlling the positions of the die 14 andinterconnect 24 by optical, optical-mechanical or other methods forvertical alignment and parallelism.

One or more ultrasonic vibration generators or transducers 44A aremounted to vibrate the die 14 and/or interconnect 24 in an axialdirection 45, i.e., parallel to centerline 42. FIG. 1 shows a firstultrasonic vibration generator 44A surrounding and attached to the quill12. The generator 44A is controllable to axially vibrate the quill 12and attached die 14.

Also shown is a second ultrasonic vibration generator or transducer 44Bunderlying support member 32 and controllable to axially vibrate thesupport member 32 and attached interconnect 24. The support member 32 isconstructed of a material such as metal, e.g., stainless steel, whichwill transmit the ultrasonic vibrational movement with minimal losses inforce, linearity or amplitude.

The second ultrasonic vibration generator 44B may alternatively bepositioned above the support member 32, i.e., adjacent the interconnect24.

The produced vibratory motion is generally a sinusoidal function oftime. The generators or transducers 44A and 44B may be separatelycontrolled to produce differing frequencies and motion amplitudes which,in combination, achieve rapid linear axial piercing of the oxide layer54 (FIG. 2) and penetration of the underlying metal 58, and goodlow-resistivity adhesion of the contact member 30 with the metal,without causing damage to any of the bond pads 22 which requires repair.

Where two generators 44A, 44B are used for vibrating the die 14 andinterconnect 24, respectively, it is preferred that they be about 90-180degrees out of synchronization, so that the motions of the die andinterconnect are opposed, i.e., alternately toward each other and awayfrom each other during a fraction of the sinusoidal curves. When 180degrees out of synchrony, the amplitude setting of both transducers maybe minimized.

In another feature, the amplitudes of the two generators 44A, 44B areset to differ such that overlapping amplitude portions result invibratory contact of the contact members 30 with the bond pads 22, eventhough the vibrators are in synchronization or minimally out ofsynchronization.

The generators 44A and/or 44B may be, for example, 25 watt generators ofabout 20-60 KHz frequency, and may be adjustable for F.M. (frequencymodulation). Where a single generator 44A or 44B is utilized, thetransmitted power controlling the vibrational amplitude is set to avalue whereby the vibrational amplitude may typically be about 5-30percent of the desired full penetration depth. Where two generators 44Aand 44B are used to vibrate both the die 14 and interconnect 24, theamplitude setpoint of each may be reduced somewhat so that the netmaximum amplitude is not excessive. Likewise, the vibratory forcestransmitted to each of the die 14 and interconnect 24 may be reduced toprevent excessive forces acting on the bond pads 22 by the contactmembers 30. The optimal power requirement will vary, depending upon thetotal number of connections to be made, as well as other factors,described infra.

Non-axial and non-linear vibrations of the die 14 and interconnect 24are largely avoided by promoting axial vibrations only, in order toprevent any tearing of the bond pads 22. Any tendency to producenon-linear or non-axial vibration may be further reduced by relativelyrigid lateral support of the die 14 and interconnect 24, or by othermeans known in the art. A known ultrasonic generator has a feedbackarrangement which reduces non-linearity.

The time required to achieve full penetration of all bond pads 22 is ofvery short duration, typically of the order of a few milliseconds, e.g.,about 5 milliseconds, up to about 200 milliseconds or more, dependingupon the design, numbers, sizes and material of contact members 30 andbond pads 22. The ultrasonic vibration force(s) and amplitude will alsoaffect the required time of ultrasonic vibration.

We turn now to FIG. 2, which is an enlarged view of portion 2 of FIG. 1.Semiconductor die 14 is shown with active surface 20. Bond pads 22 areshown mounted on the active surface 20, and the remainder of the activesurface 20 is shown covered with a passivation layer 46.

For purposes of illustration, raised interconnect contact members 30described in U.S. Pat. Nos. 5,326,428, 5,478,779 and 5,483,741 are usedin FIGS. 2 and 3 as exemplary puncture-type contact members to which theinvention is applied. In this embodiment, the contact members 30comprise raised pillars 48 having conductive caps 50 with sharp apexes52 for piercing a hard oxide layer 54 on a bond pad surface 56 andpenetrating the underlying conductive metal 58. The design of the apexes52 results in increasing resistance to penetration as the penetrationproceeds. Although each cap 50 may include a flat penetration stopsurface 60 to limit penetration, over-penetration may yet occur undercircumstances of excessive force or misalignment.

At full penetration, the apexes 52 are typically retained by the metal58 of the bond pad 22 to a degree which permits permanent use of theinterconnect-die combination. Normally, however, the interconnect is apart of a ceramic die carrier for testing an individual die, such as inKGD tests, and only temporary use is made of the connections describedherein.

As taught in the patents cited above, the interconnect 24 includesconductive traces, not visible in FIGS. 2 and 3, from each contactmember 30 to a test circuit or other circuit.

In FIG. 2, the tips 62 of the sharp apexes 52 are shown as just touchingthe oxide layer 54 on each bond pad surface 56. In the prior method offorming an electrical connection, the die 14 was subsequently compresseddownwardly in direction 40 until the tips 62 pierced the hard oxidelayer 54 and then penetrated the softer metal 58 to approximately thedesired penetration depth. A typical force-penetration curve 64 for theprior method is shown in FIG. 4. In the prior art method, the exertedcompressive force was initially increased to an oxide piercing value 66,at which point the resistance suddenly decreased, enabling adecreasingly rapid penetration. The compressive force then increaseduntil the desired “full penetration” depth 70 was attained at forcevalue 68.

Depending upon the configuration of the system, the prior artforce-penetration curve may be more like that of curve 74, i.e., wherepenetration occurs more rapidly than force reduction. As shown, themomentum of the contact member 30 may carry it to an excessivepenetration value 76.

It should be noted that in FIG. 4, curve 72 denotes a theoreticalforce-penetration relationship where there is no hard oxide layer 54 onthe bond pad 22, and penetration is through the metal only.

In the method of the invention, either or both of the die 14 andinterconnect 24 are vibrated by an ultrasonic generator 44 in axialdirection 45 (FIG. 2). The ultrasonic generators are configured to avoidor greatly minimize the production of non-axial forces which may bedetrimental to the bond pads 22. For example, piezoelectric-basedultrasonic generators exist which have feedback sensors fornon-linearity compensation.

FIG. 3 shows a bare die 14 and an interconnect 24 wherein raised contactmembers 30 on the interconnect are joined to bond pads 22 of the die.The tips 62 of the apexes 52 of the contact members 30 have pierced theoxide layer 54 and penetrated the metal 58 of the bond pads 22 to a“full penetration depth” 70. The full penetration depth 70 is less thanthe bond pad thickness 78.

The method of simultaneously forming effective bonds between a bare die14 with bond pads 22 and an interconnect 24 with raised contact members30 is as follows:

(a) the die 14 and interconnect 24 are mounted in alignment in anassembler or similar machine 10 designed to simultaneously connect theplurality of corresponding contact members and bond pads with acombination of simple compression and ultrasonic vibration;

(b) the active surface 20 of the die 14 and the connection surface 28 ofthe substrate 26 of the interconnect 24 are brought together wherebyeach contact member 30 is aligned with a corresponding bond pad 22 foraccurate connection;

(c) while compressing the die 14 and interconnect 24 together at arelatively low force, the die and/or interconnect is/are ultrasonicallyvibrated with a short burst of generally linear, axially directedvibrational energy to cause the tips 62 of the apexes 52 of the contactmembers 30 of the interconnect to pierce the oxide layer 54 on the bondpads 22 and penetrate the underlying metal 58 to the desired fullpenetration depth 70.

If the purpose of joining the die 14 and interconnect 24 is to perform abrief test, the compression force (but not the ultrasonic vibration) maybe continued until the test is complete. The die 14 and interconnect 24may then be pulled apart, either with or without the application ofultrasonic energy. In general, however, the bonding resulting from theinvention is adequate to permit withdrawal of compressive forces duringtesting and to produce bonds capable of permanence.

Turning again to FIG. 4, force-penetration curve 80 represents theeffect of using ultrasonic force to pierce the oxide layer 54 at a muchreduced applied force 82 (as compared to force 68). Ultrasonic vibrationcontinued through the metal penetration portion of the curve 80significantly reduces the compressive forces required for fullpenetration. Thus, curve 80 is seen to be at a much lower level ofcompression force than curves 64 and 74 of the prior art. Fullpenetration is achieved at the compression force level 84.

The invention has been illustrated herein using an interconnect 24 of aparticular configuration. However, the invention is applicable to aninterconnect with any puncture-type raised contact member. The term“interconnect” encompasses any substrate with such contact membersformed thereon, and may include test probes, interposers, etc.

The benefits of the invention include a lower tendency toward tearing ofthe bond pads 22, very rapid bonding of all pads 22, and greaterreliability of the bonding. It is believed that the method reduces thepossibility of damage to the piercing members, e.g., apexes 52, of thecontact members, thereby permitting greater repeated use of theinterconnect 24.

It is apparent to those skilled in the art that various changes,additions and modifications may be made in the improved die-substrateinterconnection method and apparatus as disclosed herein withoutdeparting from the spirit and scope of the invention as defined in thefollowing claims.

What is claimed is:
 1. A method for forming bonds between asemiconductor die having at least one bond pad on a first surfacethereof and an interconnect having at least one contact member on aconnection surface thereof, said at least one contact member forpenetrating a layer of material on an outer surface of said at least onebond pad for connecting said at least one contact member to said atleast one bond pad of said semiconductor die, said method comprising:aligning said semiconductor die and said interconnect; bringing togethersaid connection surface of said interconnect having said at least onecontact member aligned proximate said at least one bond pad on saidfirst surface of said semiconductor die; providing a force to at leastone of said semiconductor die and said interconnect; engaging saidsemiconductor die and said interconnect using said force; andsubstantially ultrasonically vibrating one of said semiconductor die andsaid interconnect using vibrational energy having said at least onecontact member of said interconnect penetrating a portion of said atleast one bond pad of said semiconductor die, forming an electricalconnection.
 2. The method of claim 1, whereby said engaging and saidsubstantially ultrasonically vibrating are continued having said atleast one contact member penetrating said portion of said at least onebond pad to a predetermined depth.
 3. The method of claim 2, whereinsaid predetermined depth comprises a range of about 0.3-0.8 of athickness of said at least one bond pad.
 4. The method of claim 2,wherein said substantially ultrasonically vibrating is conducted toachieve a vibrational amplitude in a range of about 5 to about 30percent of said predetermined depth.
 5. The method of claim 1, whereinsaid substantially ultrasonically vibrating is conducted in a range ofabout 5 to about 200 milliseconds.
 6. The method of claim 2, furthercomprising: detecting penetration of said at least one bond pad to saidpredetermined depth by detection/feedback apparatus.
 7. A method forforming bonds between a semiconductor die having at least one bond padon a first surface thereof and an interconnect having at least onecontact member on a connection surface thereof, said at least onecontact member for penetrating a layer of material on an outer surfaceof said at least one bond pad for connecting said at least one contactmember to said at least one bond pad of said semiconductor die, saidmethod comprising: aligning said semiconductor die and saidinterconnect; bringing together said first surface of said semiconductordie and said connection surface of said interconnect having said atleast one contact member aligned proximate said at least one bond pad onsaid first surface of said semiconductor die; providing a force to atleast one of said semiconductor die and said interconnect; engaging saidsemiconductor die and said interconnect using said force; substantiallyultrasonically vibrating one of said semiconductor die and saidinterconnect using vibrational energy having said at least one contactmember of said interconnect penetrating a portion of said at least onebond pad of said semiconductor die, forming an electrical connection,said substantially ultrasonically vibrating continuing to have said atleast one contact member penetrating said portion of said at least onebond pad to a predetermined depth; detecting penetration of said atleast one bond pad to said predetermined depth by detection/feedbackapparatus; and terminating said penetration of said at least one bondpad to said predetermined depth by said detection/feedback apparatus. 8.The method of claim 1, wherein said electrical connection comprises anonpermanent electrical connection between said at least one bond padand said at least one contact member.
 9. The method of claim 1, whereinsaid electrical connection comprises a permanent electrical connectionbetween said at least one bond pad and said at least one contact member.10. The method of claim 1, further comprising: retracting saidsemiconductor die and said interconnect from each other duringapplication of a linear axial ultrasonic vibrational force to one ofsaid semiconductor die and said interconnect, said retracting fordisconnecting said semiconductor die from said interconnect.